Burners of the kind described in the preamble may be found in stationary combustion plants where the combustion chamber is located inside e.g. a central heater. The combustion gases, generated by combustion in the combustion chamber, are arranged to be absorbed by the surrounding walls of the combustion chamber or by tubes, if any, through which the combustion gases flow which then are diverted via an exhaust pipe and e.g. through a chimney.
In order to use a burner/heater according to the preamble for other purposes than e.g. for heating of water and generation of steam but instead for the heating of surfaces, e.g. the heating of a bitumen mass when laying roofing-board, the burner has to be manageable by hand and arranged in a way that no damage or injury on account of open flames or too high temperature of the nozzles or the like appear to the roof covering or to the person who handles the device. Modern gas burners work with an open flame that is directed towards the roof covering and might easily set fire to it.
So-called heat guns in which air is heated e.g. by an electrically heated incandescent spiral work without open flame but the heating effect in normally occurring embodiments is too low to use e.g. for laying roofing-board in cool weather. In order to get an increased heating effect from an electrically heated hot-air gun an electric current is needed, which normally is not available in buildings e.g. for housings.